The present invention relates to methods and apparatus for performing a hip replacement.
Hip replacement surgery, pioneered in the early 1960's, has been characterized by the substitution of the degenerated joint with prosthetic components, typically formed of polyethlylene and metal alloys. These are affixed to the underlying bone immediately at the time of surgery by the use of bone cement or by coating or texturing the components in such a manner as to allow the surrounding bone to eventually grow into the surface. However subsequent loosening of the prosthesis, regardless of the method of fixation, has been a well documented complication of the procedure. Additionally, this loosening can become clinically symptomatic requiring revision surgery. This problem is especially concerning in younger individuals who have undergone joint replacement, as their functional demands are often higher than in older individuals and their expected lifespan may be in excess of the anticipated functional life of the replacement.
Further study of the problem of long term prosthetic loosening has suggested that the common underlying pathway of failure for cemented and uncemented prostheses involves the generation of particulate debris. That is, particles of polyethylene, submicron in size, are generated by the articulation of the two prosthetic components during motion. It is estimated that some 500,000 submicroscopic polyethylene particles are produced with each individual step that a patient takes, with as many as 1,000,000 cycles or steps per year. It has been postulated that this debris creates not only third body wear of the components, but also produces an inflammatory reaction in certain individuals resulting in the release of degradative enzymes. These enzymes can ultimately lead to a breakdown of the bone/cement or bone/prosthesis interface.
Consequently, significant effort has been directed toward reducing the production of such particles, mainly by improving the biomechanical properties of the polyethylene through manufacturing and processing techniques. As well, the use of ultra-low friction ceramics has been tried in clinical practice toward this end, however cases reports of early prosthetic fractures necessitating revision surgery has curtailed their use. A reemergence of trials of metal-on-metal articulations has also recently appeared, but no long-term data on these is available as of yet, leaving the problem of particulate debris and loosening as the single and most significant unsolved problem facing joint replacement surgeons today.
Therefore, it would be desirable to provide hip replacement methods and techniques which eliminate or alleviate the above described problems.